Mental health and addiction treatment experts praised what they described as a “historic” expansion Friday of insurance coverage for millions of Americans suffering from psychological or substance abuse problems, five years after a law requiring the coverage first passed.

But they also said they’ll be waiting to see whether a federal final rule that requires insurers to regard mental health and addiction problems on par with other illnesses actually lives up to its promises.

“This has been anxiously and long awaited,” said Dr. Jeffrey Lieberman, president of the American Psychiatric Association. “Everything we’ve heard gives us a lot of encouragement. We just hope the rule goes far enough.”